Functional Magnetic Resonance Imaging (fMRI) portrays particular parts of the brain that are active during specific activities of a subject. For example, experiments have illustrated those parts of the brain that are most active while performing mental arithmetic, or while opening and clenching a hand. Some differences have been noted between activity patterns of the mentally ill and those of “normal” subjects. fMRI operates by observing a coupled set of blood flow, volume and oxygenation changes in the brain, which are collectively termed the hemodynamic response. This hemodynamic response correlates with neuronal activity in the brain.
While the spatial resolution of fMRI is good, fMRI requires the subject's head remain stationary between poles of a magnet in a large, bulky, sometimes noisy, and usually expensive machine throughout a study. The requirement of stable head position renders fMRI impractical as a way to observe patterns of brain activity during many activities of a subject such as—for illustration and not by limitation—walking on a treadmill or, even holding an animated conversation. Further, the expense and immobility of fMRI machines precludes routine clinical use of fMRI on patients of average wealth in diagnosis and treatment monitoring of such psychiatric and neurological disorders as schizophrenia, Parkinsonism, epilepsy, multiple sclerosis, tumors, dementia, stroke rehabilitation and traumatic brain injury where it is expected that brain activity patterns may differ from the norm.
It is well known that light, including near-infrared light, penetrates to a limited extent through many human tissues, including the brain, skull and scalp; although that light is scattered by those tissues and some wavelengths are absorbed more than others. It is also well known that a pattern of absorbed wavelengths (or color) of light transmitted by tissue varies with oxygenation of blood in the tissue. Further, volume and flow of blood in the tissue is known to change scattering properties in the tissue.
Diffuse-optical functional neuroimaging is a technique of determining patterns of brain activity in mammalian or human subjects by projecting light into the subject into selected points on the subject's head while observing patterns of intensity, phase and color of scattered light emitted from the head at selected points. This may be performed using light having wavelengths in the near-infrared, with tomographic processing to obtain some three-dimensional localization of activity regions. It is expected that that brain activity patterns obtained through this near-infrared diffuse-optical functional neuroimaging (NIR-DOTFNI) can be correlated to activity patterns obtained through fMRI, and that these patterns may also correlate with brain activity patterns obtained through electroencephalography (EEG), magnetoencephalogram (MEG), transcranial Doppler sonography (TCD), positron emission tomography (PET), and single-photon emission computed tomography (SPECT).
NIR-DOTNFI is expected to provide a more portable apparatus for functional neuroimaging than possible with fMRI, thereby providing imaging useful for research, as well as diagnosing a variety of psychiatric conditions and identifying lesions including tumors in a subject. A second advantage of NIR-DOTFNI over fMRI is its superior temporal resolution over fMRI, which permits detailed quantitative analysis of the time-course of the hemodynamic response. A third advantage of NIR-DOTFNI over fMRI is its ability to determine changes in blood volume, oxygenation and flow through the use of multiple colors of laser light and spectroscopic analysis and computer modeling.
NIR-DOTNFI apparatus may also prove useful for determining truth and falsity of statements made by a suspect, although this is still a subject of research. Other potential applications of NIR-DOTNFI include, but are not limited to, brain computer interface (BCI), real-time neurofeedback for academic learning, real-time neurofeedback for rehabilitation training, acute patient monitoring in the neuro-intensive care unit, and attention monitoring for pilots and drivers.
An optode is a device for coupling light between optical or optoelectronic components (such as fiber bundles and/or lasers and/or photo-detectors) and a surface (such as skin or mucus membranes) of a subject. An optode may be used to couple light into the surface of the subject, out of the surface, or both. Optodes are typically connected to an end of a flexible light guide such as fiber-optic fibers or bundles or liquid light guides that in turn connect to light emitting devices such as lasers and/or light measuring and detecting apparatus such as photodiodes; some optodes may be used for light emission into the subject, some for light detection, and some for both. The optic fibers or bundles or liquid light guides may be bifurcated, quadfurcated, or further divided to or from the optode for the purpose of, for example, coupling multiple colors of laser light into the surface or coupling the light collected from multiple optodes into a single detector. The light emitting apparatus such as lasers and/or light measuring and detecting apparatus may be worn by the subject, or may be located several meters away.
Some optode designs have proved to be bulky, others have proved to be incompatible with EEG, MEG or fMRI, others have proved time consuming to attach to a subject, overly difficult to attach, or to be too painful to the subject for practical use.
U.S. Pat. No. 5,361,316 to Tanaka, et al., describes a probe for coupling light from an optical fiber into a body cavity for phototherapy, the probe having a ball lens. This device has no prism and does not lend itself to use as a compact optode for functional neuroimaging. A ball lens is also used in the coupling device of Schwarz, et al., Ball Lens Coupled Fiber-Optic Probe For Depth Resolved Spectroscopy Of Epithelial Tissue, Optics Letters, 15 May 2005 1159-1161. The coupling device of Schwarz lacks a prism, and has several stimulus fibers surrounding a central receive fiber in the same coupling device, and is intended to provide for infrared measurements of skin rather than deeper structures.
Hamamatsu's NIRO-200 system provides a multiple-channel device for generating infrared light, for coupling this light to an optode having a prism at the end of an optical fiber for coupling light into scalp regions without hair, and for receiving and measuring transmitted light. The prism optode design of Hamamatsu lacks any small optical component to displace the hair and make direct contact with scalp skin. This device also does not support simultaneous electroencephalography. The optodes of this device have no lens and is bulky enough to preclude the high-density optode arrays required for good resolution and accurate neuroimaging, and is bulky enough to preclude high density optode arrays combined with electroencephalographic arrays.